I completely understand how you feel about motivation. It's funny how our mind is such a powerful force in our daily decisions. How man people you know exercise and when they are finished feel worse than before? I don't know any, yet to get to the point where you put on those gym clothes and actually go do it seems to be the hardest part of the battle.
The first thing to realize is exercise, like so many other things, is a habit. And it takes awhile to form a habit. At this point it's important to schedule it into your day, and preferably if you can at the same time so you start to get used to doing 'X' exercise at 'X' time.
Second, try experimenting with all kinds of things. You don't have to hate exercising. There are SOOOOOO many different things you can do depending on what you enjoy doing. I've done everything from dance classes to pilates and yoga to weight training classes to swimming to boxing (my fav right now) and kickboxing to running to uphill walking, etc. etc. Everyone is different and when you find something you enjoy doing, it'll seem alot less like work and more like a recreational activity.
Third, give your body time to adjust to your workout routine. Don't try and go balls to the wall the first time you exercise. Your body will tell you when you are working hard and when you are working too hard. You don't want to push too hard right now, and you will still get results. Allow your body to physically adapt to your new activity.
Fourth, don't give up on yourself. You are not alone. We all have been or are going through what you are going through. Even though I have been working out 4-6 times a week since January, I STILL sometimes have to motivate myself to go workout. But now I feel horrible if I don't workout because it's just a part of my day like going to work. With consistency you will reach that point before you know it.
Goodluck and don't forget you have a family here at 3FC, the people here are just wonderful and absolutely encouraging!